1. Field of the Invention
The present invention relates generally to a wireless local area network in which parent hosts and mobile hosts are organized into several subnetworks to establish wireless links by exchanging control packets, and more specifically to the avoidance of interruption of the links due to possible movement of the mobile hosts and of radio interference between subnetworks.
2. Description of the Related Art
In a known wireless local area network, as described in Draft Standard IEEE 802.11 xe2x80x9cWireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specificationsxe2x80x9d (P802.11 D2.0, Jul. 28, 1995), a plurality of mobile hosts and a plurality of base hosts are organized into a plurality of subnetworks so that each subnetwork consists of a single base host and several mobile hosts. Channels of different frequencies arc permanently assigned to the subnetworks by taking into account their propagation environments and communication traffic. Within each subnetwork, the assigned channel is shared among its base host and its member mobile hosts. Each mobile host relies on user""s manual assistance in order to set up the assigned channel. Overall reassignment of channels is often performed whenever there is a change in propagation environment and traffic. However, with possible movement of a mobile host from one subnetwork to another, the user must check for the channel number of the new subnetwork and alter the stored channel data before establishing a link with the base host of the new subnetwork. In addition, when a mobile host suffers from interference from an adjacent subnetwork, a time-consuming channel reassignment procedure will be required.
It is therefore an object of the present invention to provide a wireless local area network where the manual assistance for mobile hosts is eliminated and channels are automatically reassigned.
In a wireless local area network, a subnetwork is formed by a home base host and a home mobile host and a wireless link is established over a selected channel between the hosts. The home mobile host may receive an interfering signal from another subnetwork. According to the present invention, a control packet is broadcast from the home parent host at periodic intervals and the mobile host monitors the control packet and the interfering signal. If the mobile host does not receive the control packet for a predetermined period or detects the interfering signal, it makes a search for a new channel. The parent host also monitors interfering signals from other subnetworks. If it detects an interfering signal, it selects a new channel. The channel number of the new channel may be broadcast using a channel assignment signal to allow the home mobile hosts to select the new channel. Alternatively, no channel assignment signal is broadcast. In this case, it is up to the home mobile hosts to hunt for a new channel.
In a preferred form of this invention, the home mobile host is arranged to transmit an acknowledgment request from the home mobile host to the home parent host if it detects interference and identifies the parent host of another subnetwork as a source of interference, transmit a channel switchover request from the mobile host to the parent host if an acknowledgment response is returned within a predetermined interval. If the acknowledgment response is not returned within the predetermined interval, the mobile host makes a search for a new channel to reestablishes communication. The home mobile host is further arranged to transmit an acknowledgment request to the home parent host if it identifies the mobile host of another subnetwork as a source of interference. If an acknowledgment response is returned within a predetermined interval, the mobile host transmits a channel switchover signal to another subnetwork to cause it to switch over to a different channel. If the acknowledgment response is not returned within the predetermined interval, the mobile host makes a search and selects a new channel.